Steering control apparatus

Abstract

Provided is a steering control apparatus configured to suppress the occurrence of abnormalities in components in respective systems at the same timing. A first assist torque calculation circuit calculates a first command value and a second command value based on a steering torque. A first current feedback control circuit calculates a control signal by using the first command value. A second current feedback control circuit calculates a control signal by using the second command value. When the steering torque is equal to or smaller than a steering torque threshold, the first assist torque calculation circuit executes calculation so that the first command value is larger than the second command value. After the steering torque exceeds the steering torque threshold, the first assist torque calculation circuit executes calculation so that the first command value is equal to the second command value.

What is claimed is: 
     
       1. A steering control apparatus configured to control a steering system configured to apply, by a motor, a driving force for reciprocating a steering operation shaft, the steering control apparatus comprising:
 a control circuit configured to cause the motor to apply a torque to a steering mechanism by calculating a command value of the applied torque based on a steering state variable including a steering torque and controlling power supply to a plurality of coils of the motor in a plurality of systems based on the command value, the plurality of coils in the plurality of systems include a first-system coil and a second-system coil, the control circuit includes:
 a first-system control circuit configured to control power supply to the first-system coil based on a first command value of a torque generated by the first-system coil; and 
 a second-system control circuit configured to control power supply to the second-system coil based on a second command value of a torque generated by the second-system coil, wherein: 
 
 the control circuit is configured to execute first control configured to set the first command value and the second command value to be different from each other when an input value, which has a correlation with a total sum of the torque generated by the first-system coil and the torque generated by the second-system coil, is equal to or less than a predetermined value, and 
 the control circuit is configured to execute second control configured to reduce a difference between the first command value and the second command value when the input value is larger than the predetermined value, as compared to a difference between the first command value and the second command value when the input value is equal to or less than the predetermined value. 
 
     
     
       2. The steering control apparatus according to  claim 1 , wherein:
 each of the first-system control circuit and the second-system control circuit includes a distribution ratio setting circuit configured to variably set, based on the input value, a distribution ratio that is a ratio between the first command value and the second command value, and 
 each of the first-system control circuit and the second-system control circuit is configured to:
 calculate a basic command value of the total sum of the torque generated by the first-system coil and the torque generated by the second-system coil; and 
 calculate the first command value and the second command value based on the basic command value and the distribution ratio. 
 
 
     
     
       3. The steering control apparatus according to  claim 2 , wherein the distribution ratio setting circuit is configured to:
 set the distribution ratio to a value larger than ½ when the first control is executed; and 
 reduce a difference between the distribution ratio and ½ when the second control is executed as compared to a difference between the distribution ratio and ½ when the first control is executed. 
 
     
     
       4. The steering control apparatus according to  claim 2 , wherein the distribution ratio setting circuit is configured to set the distribution ratio so that the first command value is larger than an equalized command value obtained by equally distributing the basic command value, and the second command value is smaller than the equalized command value when the first control is executed. 
     
     
       5. The steering control apparatus according to  claim 4 , wherein the distribution ratio setting circuit is configured to set the distribution ratio so that the first command value and the second command value are closer to the equalized command value as the input value is closer to the predetermined value when the first control is executed. 
     
     
       6. The steering control apparatus according to  claim 3 , wherein at least one of the first-system control circuit and the second-system control circuit is configured to, when the first control is executed:
 determine whether a sum of the first command value and the second command value is equal to the basic command value and whether the first command value and the second command value have a same sign; and 
 stop the first control when the sum of the first command value and the second command value is not equal to the basic command value or when the first command value and the second command value do not have the same sign. 
 
     
     
       7. The steering control apparatus according to  claim 1 , wherein, in the second control, the first command value and the second command value are set equal to each other.